Hydraulic system



April 1949- w. c. TRAUTMAN I 2,467,508

HYDRAULIC SYSTEM Filed Nov. 28, 194

INVENTOR.

-W.IC.TRAUTMAN ATTORNEY MHI Patented Apr. 19, 1949 STATES PATENHYDRAULKC SYSTEM Application November 28, 1944, Serial No. 565,538

(ill. 60-52) 3 Giairns.

This invention relates to hydraulic actuating systems in which pressurefluid is supplied to either end of a motor cylinder by areversible pumpand has to do more particularly with systems of this type in which themotor cylinder contains a piston connected to a device to be actuated bya piston rod which extends from the piston through one end only of thecylinder, so that the displacement of the piston is less on the pistonrod side than on the other side.

An object of the invention is to provide a simple ment end of the motorcylinder, in combination and efi'ective means for compensating for thediflerent displacements in the opposite ends of a motor cylindersupplied with pressure fluid by a reversible pump.

Another object is to provide a hydraulic actuating system employing amotor cylinder actuated by a reversible pump driven by a reversibleelectric motor in which the electric motor is automatically controlledto maintain pressure to hold the piston of the motor cylinder in aposition into which it has been actuated.

Other more specific objects and features of the invention will appearfrom the description to follow of a specific embodiment of theinvention.

It is frequently desirable to supply pressure fluid to one end of amotor cylinder and exhaust fluid from the other end by means of areversible pump driven by a reversible electric motor. Such a system hasthe advantage that the usual fourway control valve between the pump andthe motor can be eliminated and the entire control effected by merelyrunning the electric motor in one direction or the other. However, insuch systems, the hydraulic motor cylinder usually has a piston rodextending through one end of the cylinder so that the fluid displacementis difierent in the two ends of the cylinder, whereas the reversiblepump displaces fluid at the same rate through its inlet and outletports. The present invention resides in the addition to a system of thetype described of a particularly simple and eii'ective automatic valvearrangement for exhausting excess fluid from the large displacement endof the motor cylinder when pressure fluid is being supplied by the pumpto the small displacement end of the motor cylinder, and for supplyingadditional fluid to the in-take side of the pump when the latter isdelivering pressure fluid to the large displacement end of the motorcylinder.

V Essentially, my system includes a simple check valve for admittingextra fluid to the port'of the pump that is the in-take port when thepump is delivering pressure fluid to the large displacewith anothervalve for automatically connecting the large displacement end of themotor cylinder to the reservoir when the pump is supplying pressurefluid to the small displacement end of the 'motor cylinder.

A practical embodiment of the arrangement outlined and including variousdetails of construction will now be described with reference to thedrawing, in which:

Fig. 1 is a schematic diagram of a system in accordance with theinvention with its various elements shown in the positions they occupywhen the motor is running in one direction and;

Fig. 2 is a similar view showing the parts in the positions they occupywhen the motor is running in the other direction.

Referring first to Fig. 1, there is shown a hydraulic motor cylinder I0containing a piston ll having a piston rod l2, which extends through theleft end of the cylinder II], for connection to a device to be actuated.By virtue of the'existance of the piston rod l2, the movement of thepiston ll results in a larger displacement of fluid in the right end ofthe cylinder than in the left end. The right end of the cylinder isconnected, through a conduit [3 and through a locking valve M, to aconduit l5 which extends to one port of a reversible pump H5. The leftend of the cylinder I 0 is connected through a conduit l1 and throughthe locking valve I4, to a conduit I8 which connects to the other port,of the pump 16. The motor piston II] can be driven in either directionby driving the reversible pump iii in one direction or the other.

The pump l6 may be of any known construction, but is shown as a gearpump having two intermeshing gears l9, one of which is directlyconnected to the shaft of an electric motor 20, which is adapted to berotated in one direction by closure of a switch 2|, and in the oppositedirection by closure of a switch 22. As is clearly shown in the diagram,the motor is of the threephase type supplied from a three-phase line23!, and the direction of rotation of the motor is re-' versed byreversing any two of the three leads, as is well-known in the art.

The pump l6 ejects from its outlet port theplacement of the left end ofthe cylinder II a lesser flow of fluid is being delivered from thecylinder through conduits I1 and I3 to the inlet of the pump. If noprovision were made for the supply of additional fluid to conduit I3,the operation of the pump would be impaired. In accordance with thepresent invention, the fluid defliciency is made up by providing abranch conduit 23 containing a simple check valve 24 interposed betweenthe conduit I3 and a fluid reservoir 25. The check valve 24 preferablyhas a relatively light spring, so that only a very slight reduction ofthe pressure in conduit I3 below the atmospheric or ambient pressure issuiflcient to open the check valve and permit flow of as much fluid asis necessary to compensate for the diflferent displacements of the twoends of the motor cylinder, and maintain the inlet port of the pumpfllled with fluid at all times.

The conditions existing when the pump is driven in the reverse directionare illustrated in Fig.

2. In this case, the pump I5 is delivering fluid to the conduit I3, andthe pressure therein closes the check valve 24 so that there can be noescape of fluid therethrough to the reservoir 25. The fluid delivered bythe pump flows through the conduit |3,- the valve I4, and the conduit Ilinto the left end of the motor cylinder III, to move the piston II tothe right. This results in the exhaust of a larger amount of fluid fromthe right end of the cylinder, which fluid flows back through theconduit I3, the valve I4, and the conduit I5. Obviously, since the flowof the fluid into conduit I5 from the motor I0 exceeds the flow beingdelivered by the pump I5, it cannot all return to the pump, and theexcess fluid flows through a branch conduit 21, through'a valve 23, intoan exhaust conduit 29, and through a filter 30, into the reservoir 25.

The valve 23 is normally closed, and is held closed by pressure inconduit I5, but opens in response to pressure in conduit l3. Thus, thevalve comprises a casing 3| having a partition therein defining a valveseat 32 which is normally closed by a poppet 33 urged toward the seat 32by a compression spring 34. The right end of the casing 3| to the rightof the valve seat 32 constitutes a cylinder and contains a piston 35having a stem 35 which presses the poppet 33 open when the piston 35moves to the left. The left end of the piston 35 is, at all times,exposed only to the low pressure existing in the exhaust conduit 23,whereas the right end of the piston 35 is exposed to the pressureexisting in conduit I3, the right end of the casing 3| being connectedto the conduit I3 by a branch conduit 31. A compression spring 33 movesthe piston 35 to the right into the position shown in Fig; 1, exceptwhen pressure fluid is being supplied to the conduit I3 as shown in Fig.2.

It is obvious from the foregoing description that whenever the pump isbeing operated in the direction to supply pressure fluid to conduit I5,as shown in Fig. 1, the poppet 33 is held on its seat by the spring 34and the pressure in conduit I5, so that the full output of the pump isdelivered to the right end of the motor cylinder I3; at the same timethe suction in the conduit I3 opens the check valve 24 to permit flow ofthe necessary make-up fluid to inlet of the pump.

On the other hand, whenever the pump is running in the oppositedirection to supply pressure fluid to conduit I3, as shown in Fig. 2,the check valve 24' is closed so that the full output of the pump isdelivered to the left end of the motor cylinder I3, and poppet 33 isopened by the piston 35 to by-pass excess fluid from the conduit I5 backto the reservoir 25.

As shown in the drawing, the locking valve I4 is provided in both theconduits leading to the motor cylinder III. Such valves are not broadlynew. but it is believed that the use thereof in this particular systemin combination with the control system to be described constitutesinvention.

The valve I4 includes casing means deflning a cylinder 43 opposite endsof which cylinder are connected to the conduits I3 and I5 respectively,and the cylinder contains a piston 4|. Opposite ends of the cylinder 43have valve seats 42 and 43 therein, both of which are closed by poppets44 and 45 respectively when there is no differential pressure betweenthe conduits I5 and I3. Thus, poppets 44 and 45 are constantly urgedagainst their seats by compression springs 45, and these springsfunction to seat the poppets whenever the pump I5 is not running and thepressures in the conduits I5 and I3 are substantially equal, and low.However, whenever the pressure in either conduit I5 or I3 exceeds thepressure in the other conduit, which condition prevails whenever thepump is running, the piston 4| is shifted by the differential fluidpressure against the force exerted by centering springs 41, and one oftwo stems 43 extending from the piston opens one of the other of thepoppets 44 or 45. The same pressure differential that shifts the piston4| to open one of the poppets automatically opens the other poppet, thelatter functioning as a check valve. Thus, under the conditionsprevailing in Fig. 1 in which the pressure is high in conduit I5 and lowin conduit II, the piston H is moved to the left to open poppet 44, andthe pressure in conduit I5 acts directly on poppet 45 to open it.

40 On the other hand, when fluid is being supplied by the pump toconduit I3 and exhausted from conduit I5, the pressure is high inconduit I3, and the piston 4| is moved to the right to open poppet 45,and the pressure in conduit I3 functions directly to open poppet 44. Thenet result is that whenever the pump is running, in either direction,both poppets 44 and 45 are off their seats, but whenever the pump andthe flow stop, the pressure equalizes in the conduits I5 and I3, andboth the poppets 44 and 45 seat immediately to maintain pressure in theconduits I3 and I1 and hold the motor piston I in the position in whichit has been moved.

The system disclosed is so arranged that the pump is automaticallyoperated to move and maintain the piston II in one end position or theother depending upon the position of a coptrol switch 53, which connectsa source of current 5| either to a solenoid 52 which closes the switch2|, or to a solenoid 53 which closes the switch 22. These circuits fromswitch 53 to the solenoids 52 and" are completed through a pair ofpressure switches 55 and 54 which are connected to conduits I3 and I1respectively and open their contacts whenever the pressure in theassociated conduit exceeds a predetermined magcontacts 51 and 58,whereas when the pressure exceeds a predetermined value the piston 60 ismoved upwardly to lift the bar 56 and break the circuit.

The pressure switch 55 is connected in series with the left contact 63of the control switch 50. and the pressure switch 54 is connected inseries with the right contact 64 of switch 50.

The operation of the system may be briefly traced as follows:

Assumed that it is desired to move the motor piston II to the left, thecontrol switch 50 is moved to the left to close with contact 63, asshown in Fig. 1. This completes a circuit through the pressure switch 55to the solenoid 52, energizing the latter to close the power switch 2!and cause the motor 20 to rotate the pump in the direction indicated bythe arrows thereon. The rotation of the pump develops pressure inconduit l5 which moves the piston Iii in the locking valve id to theleft, and also opens the poppet 65, so that the pressure fluid flowsthrough into conduit is and into the right end of the motor cylinder H],moving the piston I l to the left. The pressure switch 55 is adjusted toopen only in response to pressures in the conduit l3 in excess of thepressures required to move the piston ii and whatever device it drives.Hence, the pressure switch does not open during movement of the motorpiston, and the action continues, the fluid from the left end of thecylinder I being exhausted through the conduit [1 past the open poppet44 into conduit l8 and back to the inlet port of the pump, make-up fluidbeing supplied from the reservoir 25 through the check valve 24 aspreviously described. When the piston ll reaches the left end of itsstroke, the pressure in conduits I and I3 immediately rises to arelatively high value at which the pressure switch 55 Operates to openthe circuit to the solenoid 52; it in turn permits the switch 2| to openand stop the motor and the pump. As the pump decelerates, the pressurein conduit l5 drops, but the pressure'is held in conduit l3 because thepoppet 45 closes in response to any tendency toward reverse flow fromconduit I 3 into conduit I5. Hence, the pressure switch 55 remains open.If there is no leakage and no reduction in temperature, the pressureconduit l3 may remain high enough to keep the pressure switch 55 openuntil such time as the switch 50 is moved to the right to shift themotor piston to the right. However, if as a result of leakage or a dropin temperature the pressure in conduit I3 drops below a predeterminedvalue, the pressure switch 55 will again close its contacts to start thepump and run it long enough to again build the pressure up to the valueat which the pressure switch opens. Hence, even if the system is leftfor a long period of time, the motor and pump start and stopautomatically, if necessary, to maintain the pressure holding the motorpiston I I in its left position.

When it is desired to move the motor piston H into the right end of itsstroke, the switch is thrown to the right as shown in Fig. 2 whereupon acircuit is completed through contact 64 and through pressure switch 54to energize the solenoid 53 and close the switch 22 to run the electricmotor and the pump in the opposite direction, as indicated in Fig. 2.Under these conditions, pressure fluid is supplied to conduitl8, whichmoves the piston in the locking valve M to the right, and opens thepoppet 44 to permit the fluid flow into the left end of the cylinder 76I. At the same time: fluid is exhausted from the right end of the motorcylinder l0 past the poppet valve 45, since the latter is now held openby piston 4|. The excess fluid is by-passed back to the reservoirthrough the valve 28 as previously described. When the motor pistoncompletes its stroke, the pressure rapidly rises in the conduit l I, toopen the pressure switch 56 and stop the motor and pump, whereupon thepoppet M in the locking valve closes to maintain the pressure in theconduit l1. Should this pressure drop below the predetermined value, theelectric motor will again be started up, and will run the pump longenough to rebuild the pressure to the desired value.

A handwheel 20a is provided on the motor 20 to permit operation of thepump in an emergency if the power supply should fail.

A pressure relief valve 70 is preferably provided between the conduits Hand I3 and the exhaust conduit 29, to relieve excessive pressures thatmay develop in either conduit H or it as a result of a rise intemperature. The relief valves are so adjusted that they do not operatein normal service. They function to prevent damage to the system in theevent of a temperature rise or in the event the electric motor shouldnot shut down for any reason, such as stuck switches or relays.

The electrical control means for the system is covered by divisionalapplication, Serial Number 640,001, filed January 9, 1946,

Although for the purpose of explaining the invention a specificembodiment thereof has been described in detail various departures fromthe exact construction shown can be made without departing from theinvention, which is to be limited only to the extent set forth in theappended claims.

' I claim:

1. In a hydraulic actuating system, a motor cylinder and piston having apiston rod extending from the piston through one end only of thecylinder, whereby the piston displaces less fluid on the rod side thanon the other side, a fluid reservoir, a reversible pump having twoports, one of which is an inlet port, and the other an outlet port whenthe pump runs in one direction and vice versa when the pump runs in theother direction, first conduit means connecting one of said pump portsto said rod end of said cylinder, second conduit means connecting theother pump port to the other end of said cylinder, and means forequalizing fluid flow through said pump ports comprising: a firstconnection including check valve means between said reservoir and saidfirst conduit means for permitting fluid flow directly to said firstconduit means from said reservoir and preventing fiow from said firstconduit means to said reservoir, a normally closed poppet valve directlyconnected between said reservoir and said second conduit means, andpressure responsive means for opening said valve in response to pressurein excess of a predetermined value in said first conduit means, saidnormally closed valve being a poppet valve having a popp t adapted to beurged against its seat by pressure in said second conduit means, andsaid pressure responsive means comprising means for lifting said poppetoff its seat.

2. In a hydraulic actuating system, a motor cylinder and piston having apiston rod extending from the piston through one end only of thecylinder, whereby the piston displaces less fluid on the rod side thanon the other side, a fluid reservoir, a reversible pump having twoports, one

emos 7 at which is an inlet port, and the other an outlet port when thepump runs in one direction and vice versa when the pump runs in theother direction, first conduit means connecting one of said pump portsto said rod end of said cylinder, second conduit means connecting theother pump port to the other end of said cylinder, and means forequalizing fluid flow through said pump ports comprising: a firstconnection including check valve means between said reservoir and saidfirst conduit means for permitting fluid flow directly to said firstconduit means from said reservoir and preventing flow from said firstconduit means to said reservoir, a normally closed poppet valve directlyconnected between said reservoir and said second conduit means, andpressure responsive means for opening said valve in response to pressurein excess of a predetermined value in said first conduit means, saidnormally closed valve and the pressure responsive means for opening itcomprising: a unitary casing having a partition therein defining a valveseat, a poppet chamber in said casing on one side of said partitioncontaining a poppet valve, said popp t chamber being connected to saidsecond conduit means, said casing including on the other side oi saidpartition a cylindrical chamber the outer end of which is connected tosaid first conduit means and the inner end of which is connected to saidreservoir, a piston in said cylindrical chamber, and means actuated bysaid piston for unseating said poppet valve in response to pressure insaid first conduit means, said poppet chamber and the inner end of thecylindrical chamber being connected when said poppet valve is unseated.

3. In a hydraulic actuating system, a motor cylinder and piston having apiston rod extending from the piston through one end only of thecylinder, whereby the piston displaces less fluid on the rod side thanon the other side, a fluid reservoir, a reversible pump having twoports, one of which is an inlet port, and the other an outlet port whenthe pump runs in one direction and vice versa when the pump runs in theother direction, first conduit means connecting one of said pump portsto said rod end of said cylinder, second conduit means connecting theother pump port to the other end of said cylinder, and means forequalizing fluid flow through said pump ports comprising: a firstconnection including check valve means between said reservoir and saidfirst conduit means for permitting fluid flow directly to said firstconduit means from said reservoir and preventing flow from said firstconduit means to said reservoir, a normally closed p p t valve directlyconnected between said reservoir and said second conduit means, andpressure responsive means for opening said valve in response to pressurein excess of a predetermined value in said first conduit means, saidnormally closed valve and the pressure responsive means for opening itcomprising: a unitary casing having a partition therein defining a valveseat, a poppet chamber in said casing on one side of said partitioncontaining a poppet valve, said poppet chamber being connected to saidsecond conduit means, said casing including on the other side of saidpartition a cylindrical chamber the outer end of which is connected tosaid first conduit means and the inner end of which is connected to saidreservoir, and a piston in said cylindrical chamber for unseating saidpoppet valve in response to pressure in said first conduit means, andspring means urging said poppet valve to closed position, said poppetchamber and the inner end of the cylindrical chamber beinginterconnected by unseating of said poppet valve.

WALTER c. TRAUTMAN.

REFERENCES CITED The following references are of record in the file .ofthis patent:

UNITED STATES PATENTS Number Name Date 1,590,226 Boisset June 29, 19261,638,653 Cannon Aug. 9, 1927 1,760,915 Robson June 3, 1930 1,955, 54Temple Apr. 17, 1934 1,956,758 Ernst May 1, 1934 FOREIGN PATENTS NumberCountry 7 Date 482,102 Germany Nov. 11, 1929

